Nonsense Suppressing Drugs for Rett Syndrome Rett syndrome (RTT) is a devastating genetic condition that affects mostly females. It is one of the worst types of neurodevelopmental disorders: the affected girls are born without any obvious problems, develop in a seemingly typical manner for the first year of life, but then abruptly and without warning lose most of their acquired abilities. RTT girls then typically develop irregular breathing patterns, fail to develop speech, lose purposeful hand movements, begin showing autism-like behaviors, frequently develop epilepsy, and often have difficulty eating and digesting food. RTT individuals exhibit a highly variable lifespan, and are at risk for sudden an unexpected death. At present there are no effective treatments or cures, despite the prevalence of RTT being more common than the rate of paralytic spinal cord injury in the general population (~1:15,000 world-wide). The majority of Rett syndrome cases are caused by mutations of the X-linked gene encoding methyl-CPG-binding protein 2 (MECP2). Proper function of MeCP2 is essential for normal nerve function, and is required for CNS maturation. Importantly, the condition is not irremediable: restoring MeCP2 function in already symptomatic MeCP2-deficient mice rescues their RTT-like condition. This observation highlights the need to develop treatment strategies that can restore MeCP2 function in affected individuals. Drugs that facilitate ?read-through? of nonsense mutations of MECP2 represent an attractive possible treatment strategy and based on our preliminary data we are convinced that effective nonsense suppressing drugs can be developed to allow successful treatment of approximately one-third of all RTT cases. The goals of this project are to develop new ?read-through? drugs with better efficacy and lower toxicity. To accomplish these goals we will carry out the following aims: (1) Identify and/or generate new ?read-through? drugs with improved properties for CNS applications by using rational drug design methods starting from selected RT ligands that we have shown to be capable of inducing expression of the MeCP2 protein. (2) Determine ?read-through? efficacies and assess the functionality of the restored MeCP2 protein. The novel drugs from Aim 1 will be tested for ?read-through? activity against the six most common MECP2 nonsense mutations seen clinically using in vitro transfection assays in HEK293 cells. (3) Determine ADME properties of analogs including brain PK, Caco-2 permeability, Cyp inhibition, microsomal stability, Ames and hERG activity. (4) Determine in vivo ?read-through? activity of analogs in brain. The top ?read-through? analogs displaying the best in vitro efficacy from Aim 2 and brain penetrance values from Aim 3 will be tested for brain activity in vivo using a custom nonsense mutation mouse model.